In order for many bodies of water to develop and maintain a healthy eco-system, a non-specific amount of circulation is typically required. This is because many of the bacteria that are necessary for breaking down or digesting nutrients are immobile, and therefore, need to be placed in intimate contact with nutrients, necessary to thrive, by circulation of the water. Furthermore, in the majority of applications, bacteria also need oxygen to survive and flourish. The most readily available source of oxygen is from the atmosphere.
Oxygen can enter the water through contact with the atmosphere which may be accelerated through mixing, as happens in nature through waterfalls, streams, rain, and wind. It has been found that adding artificial aeration, to assist nature, to natural and man made ponds and lagoons can greatly increase the health of the ponds. This may be especially useful in sewage lagoons and the like as the decay process could be accelerated and unpleasant smells reduced.
In order to combine the movement of liquid and supplying of the oxygen, past prior art has typically used one of three methods: (1) a surface splashing action (2) an aspirator/boat prop effect which draws atmospheric air in and then forces air bubbles out or (3) compressing atmospheric air and then releasing it at the bottom of the body of liquid. In each of these actions two things are readily apparent (A) high energy input with corresponding high maintenance needs and (B) the action created is always turbulent.
The use of pond aerators on floating bases has been well established such as those shown by U.S. Pat. No. 4,179,243 granted to Aide and U.S. Pat. No. 4,030,859 granted to Henager. In these patents, devices are typically supplied with a draft tube placed just below the surface of the water. This tube houses a propeller or impeller that is connected to a drive means. A draft line is placed at a predetermined depth and connected to the draft tube. Thus, as the drive means turns, the impeller or propeller draws water from a certain depth and defuses it at the water surface. This process circulates and turns the water in the pond. As power to the pump can be a significant issue in remote areas, such as the middle of a pond or lake, the efficiency of the whole unit is crucial to its success. This has required that alternative means of driving the pump on pond mixers would be desirable. One solution has been to use wind power, however wind powered pumps are large in size, expensive, cumbersome, and create a need for complex and expensive anchoring systems.
A floating water circulation apparatus is described in International Publication No. WO 00/71475 A1, that was published on Nov. 30, 2000, and that is entitled “Water Circulation Apparatus System and Method” (hereafter “System”). The System has some limitations in certain environments that are reduced or removed with the present invention. In order to understand the significance of the present invention, the principle functions of the System warrant a brief review.
The System generally relates to an aeration system for lakes and ponds and is specifically designed as a floating device which draws oxygen-depleted water from the depths of the ponds to the surface where it is set in motion on the surface and where the thin surface layer of water will absorb oxygen from the air (reaeration).
The System is essentially a solar powered floating hydraulic pump. One unique aspect of the System is in the manner in which the discharge is distributed by a distribution dish. The head required, and therefore the horsepower, for the effective distribution is less than one inch. The combined effect of the conical shape of the distribution dish, the orientation and the width of the lip on the distribution dish, and the position and operating speed of an impeller that is also utilized by the System, produce near-laminar flow on the surface. In this mode, the discharged water flows radially outward in thin successive sheets over the surface of the pond or lake in near frictionless fashion (laminar flow) to the pond embankment. When this surface layer is initially depleted of oxygen, it will, as it progresses across the pond, become saturated with pure oxygen by exposure to the atmosphere.
At the embankment, the laminar flow on the surface establishes a shallow head, causing the water to descend to the depth at which an intake screen of the System is set. At this depth the water migrates radially inward to the intake screen in a horizontal zone which is somewhat wider than the vertical distance across the intake screen (18 inches) that is attached to an intake draft tube of the System. The intake draft tube is flexible and while the intake screen may be raised or lowered, the intake draft tube will often block or inhibit omnidirectional flows to the intake screen.
The volume of liquid pumped directly by the solar powered impeller utilized by the System may be characterized as a Direct Mechanical Displacement (DMD), and in relation to the System is defined as the volume of water that is drawn into its intake draft tube and discharged over the edge of its distribution dish over a given amount of time. The DMD is measured in gallons per minute. In the case of the System, the value of the DMD is a function of the diameter and total internal friction of its intake tube, the diameter and pitch of its impeller, the slope of the sides of its conical shaped distribution dish, the depth of the impeller beneath the surface, the depth of the edge of its distribution dish with respect to the surface of the pond, and the shaft-horsepower (and resultant revolutions per minute) applied to its impeller.
The DMD produced by the System induces additional currents in the pond that are directly dependent upon the DMD. In its progression across the pond, the thin surface layer, with its higher velocity relative to the water beneath it and diverging streamlines (relative direction of flows), create a pressure differential which results in upward currents in the water beneath the surface that are referred to in International Publication No. WO 00/71475 A1 as “induced flows”. Eventually, through the combination of DMD and induced flows, the entire pond volume between the depth of the lowest point of openings in the intake screen and the pond surface becomes mixed. Provided oxygen-depleted water continues to enter the intake draft tube, the pond in which the System is operating will absorb greater quantities of oxygen from the air than would otherwise be provided by unassisted natural forces.
Once absorbed in the surface layer, which happens relatively quickly (30–40 seconds), the oxygen begins to diffuse downward. Compared to the rate at which oxygen from the atmosphere is transferred into the surface layer, the speed of diffusion is relatively slow and is dependent upon the gradient of oxygen depleted water beneath the surface and upon mixing action. The rate of diffusion is therefore the controlling function. The volume of oxygen absorbed is directly proportional to the size of the surface area of the oxygen-depleted water layer. The size of the surface layer increases with the square of the distance the laminar flow has proceeded (at the rate of about 1'/sec.) from the distribution dish. The volume of reaeration therefore depends upon time and distance from the distribution dish. Likewise, the rate of diffusion, which depends upon the supply, in this case, reaeration, and the demand (relative depletion) in the water below, the total oxygen transfer via reaeration effects by the System require some distance to become appreciable. Experience with the System has shown that the combined effects of reaeration and diffusion is not fully optimized at distances of less than 100 feet from the distribution dish, when the impeller is consistently rotating within the range of 75–115 RPM.
Because the supply of oxygen by reaeration is a function of the degree of surface area, oxygen-depletion, rate of mixing, as well as atmospheric conditions, the efficiency of the System is dependent upon the environment in which it may be located. Its beneficial effects are severely limited when operating in a pond with a small surface area (less than 1 acre) and when the rate of oxygen uptake by biological and chemical reactions in the pond exceed the rate of supply through natural reaeration. Also, under these conditions, the distribution dish of the System eventually fouls due to plant growth, reducing its efficiency.